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Fixed MTP to work with TWRP
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awab228
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267
Documentation/parport.txt
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267
Documentation/parport.txt
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The `parport' code provides parallel-port support under Linux. This
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includes the ability to share one port between multiple device
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drivers.
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You can pass parameters to the parport code to override its automatic
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detection of your hardware. This is particularly useful if you want
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to use IRQs, since in general these can't be autoprobed successfully.
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By default IRQs are not used even if they _can_ be probed. This is
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because there are a lot of people using the same IRQ for their
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parallel port and a sound card or network card.
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The parport code is split into two parts: generic (which deals with
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port-sharing) and architecture-dependent (which deals with actually
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using the port).
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Parport as modules
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==================
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If you load the parport code as a module, say
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# insmod parport
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to load the generic parport code. You then must load the
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architecture-dependent code with (for example):
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# insmod parport_pc io=0x3bc,0x378,0x278 irq=none,7,auto
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to tell the parport code that you want three PC-style ports, one at
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0x3bc with no IRQ, one at 0x378 using IRQ 7, and one at 0x278 with an
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auto-detected IRQ. Currently, PC-style (parport_pc), Sun `bpp',
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Amiga, Atari, and MFC3 hardware is supported.
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PCI parallel I/O card support comes from parport_pc. Base I/O
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addresses should not be specified for supported PCI cards since they
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are automatically detected.
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modprobe
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--------
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If you use modprobe , you will find it useful to add lines as below to a
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configuration file in /etc/modprobe.d/ directory:.
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alias parport_lowlevel parport_pc
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options parport_pc io=0x378,0x278 irq=7,auto
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modprobe will load parport_pc (with the options "io=0x378,0x278 irq=7,auto")
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whenever a parallel port device driver (such as lp) is loaded.
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Note that these are example lines only! You shouldn't in general need
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to specify any options to parport_pc in order to be able to use a
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parallel port.
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Parport probe [optional]
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-------------
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In 2.2 kernels there was a module called parport_probe, which was used
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for collecting IEEE 1284 device ID information. This has now been
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enhanced and now lives with the IEEE 1284 support. When a parallel
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port is detected, the devices that are connected to it are analysed,
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and information is logged like this:
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parport0: Printer, BJC-210 (Canon)
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The probe information is available from files in /proc/sys/dev/parport/.
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Parport linked into the kernel statically
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=========================================
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If you compile the parport code into the kernel, then you can use
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kernel boot parameters to get the same effect. Add something like the
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following to your LILO command line:
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parport=0x3bc parport=0x378,7 parport=0x278,auto,nofifo
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You can have many `parport=...' statements, one for each port you want
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to add. Adding `parport=0' to the kernel command-line will disable
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parport support entirely. Adding `parport=auto' to the kernel
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command-line will make parport use any IRQ lines or DMA channels that
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it auto-detects.
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Files in /proc
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==============
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If you have configured the /proc filesystem into your kernel, you will
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see a new directory entry: /proc/sys/dev/parport. In there will be a
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directory entry for each parallel port for which parport is
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configured. In each of those directories are a collection of files
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describing that parallel port.
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The /proc/sys/dev/parport directory tree looks like:
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parport
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|-- default
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| |-- spintime
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| `-- timeslice
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|-- parport0
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| |-- autoprobe
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| |-- autoprobe0
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| |-- autoprobe1
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| |-- autoprobe2
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| |-- autoprobe3
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| |-- devices
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| | |-- active
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| | `-- lp
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| | `-- timeslice
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| |-- base-addr
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| |-- irq
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| |-- dma
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| |-- modes
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| `-- spintime
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`-- parport1
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|-- autoprobe
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|-- autoprobe0
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|-- autoprobe1
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|-- autoprobe2
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|-- autoprobe3
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|-- devices
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| |-- active
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| `-- ppa
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| `-- timeslice
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|-- base-addr
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|-- irq
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|-- dma
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|-- modes
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`-- spintime
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File: Contents:
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devices/active A list of the device drivers using that port. A "+"
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will appear by the name of the device currently using
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the port (it might not appear against any). The
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string "none" means that there are no device drivers
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using that port.
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base-addr Parallel port's base address, or addresses if the port
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has more than one in which case they are separated
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with tabs. These values might not have any sensible
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meaning for some ports.
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irq Parallel port's IRQ, or -1 if none is being used.
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dma Parallel port's DMA channel, or -1 if none is being
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used.
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modes Parallel port's hardware modes, comma-separated,
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meaning:
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PCSPP PC-style SPP registers are available.
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TRISTATE Port is bidirectional.
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COMPAT Hardware acceleration for printers is
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available and will be used.
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EPP Hardware acceleration for EPP protocol
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is available and will be used.
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ECP Hardware acceleration for ECP protocol
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is available and will be used.
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DMA DMA is available and will be used.
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Note that the current implementation will only take
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advantage of COMPAT and ECP modes if it has an IRQ
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line to use.
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autoprobe Any IEEE-1284 device ID information that has been
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acquired from the (non-IEEE 1284.3) device.
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autoprobe[0-3] IEEE 1284 device ID information retrieved from
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daisy-chain devices that conform to IEEE 1284.3.
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spintime The number of microseconds to busy-loop while waiting
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for the peripheral to respond. You might find that
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adjusting this improves performance, depending on your
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peripherals. This is a port-wide setting, i.e. it
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applies to all devices on a particular port.
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timeslice The number of milliseconds that a device driver is
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allowed to keep a port claimed for. This is advisory,
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and driver can ignore it if it must.
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default/* The defaults for spintime and timeslice. When a new
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port is registered, it picks up the default spintime.
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When a new device is registered, it picks up the
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default timeslice.
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Device drivers
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==============
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Once the parport code is initialised, you can attach device drivers to
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specific ports. Normally this happens automatically; if the lp driver
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is loaded it will create one lp device for each port found. You can
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override this, though, by using parameters either when you load the lp
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driver:
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# insmod lp parport=0,2
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or on the LILO command line:
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lp=parport0 lp=parport2
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Both the above examples would inform lp that you want /dev/lp0 to be
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the first parallel port, and /dev/lp1 to be the _third_ parallel port,
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with no lp device associated with the second port (parport1). Note
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that this is different to the way older kernels worked; there used to
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be a static association between the I/O port address and the device
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name, so /dev/lp0 was always the port at 0x3bc. This is no longer the
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case - if you only have one port, it will default to being /dev/lp0,
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regardless of base address.
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Also:
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* If you selected the IEEE 1284 support at compile time, you can say
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`lp=auto' on the kernel command line, and lp will create devices
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only for those ports that seem to have printers attached.
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* If you give PLIP the `timid' parameter, either with `plip=timid' on
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the command line, or with `insmod plip timid=1' when using modules,
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it will avoid any ports that seem to be in use by other devices.
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* IRQ autoprobing works only for a few port types at the moment.
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Reporting printer problems with parport
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=======================================
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If you are having problems printing, please go through these steps to
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try to narrow down where the problem area is.
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When reporting problems with parport, really you need to give all of
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the messages that parport_pc spits out when it initialises. There are
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several code paths:
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o polling
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o interrupt-driven, protocol in software
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o interrupt-driven, protocol in hardware using PIO
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o interrupt-driven, protocol in hardware using DMA
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The kernel messages that parport_pc logs give an indication of which
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code path is being used. (They could be a lot better actually..)
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For normal printer protocol, having IEEE 1284 modes enabled or not
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should not make a difference.
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To turn off the 'protocol in hardware' code paths, disable
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CONFIG_PARPORT_PC_FIFO. Note that when they are enabled they are not
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necessarily _used_; it depends on whether the hardware is available,
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enabled by the BIOS, and detected by the driver.
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So, to start with, disable CONFIG_PARPORT_PC_FIFO, and load parport_pc
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with 'irq=none'. See if printing works then. It really should,
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because this is the simplest code path.
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If that works fine, try with 'io=0x378 irq=7' (adjust for your
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hardware), to make it use interrupt-driven in-software protocol.
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If _that_ works fine, then one of the hardware modes isn't working
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right. Enable CONFIG_PARPORT_PC_FIFO (no, it isn't a module option,
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and yes, it should be), set the port to ECP mode in the BIOS and note
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the DMA channel, and try with:
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io=0x378 irq=7 dma=none (for PIO)
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io=0x378 irq=7 dma=3 (for DMA)
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--
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philb@gnu.org
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tim@cyberelk.net
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